Governing of free piston type internal-combustion compressors with respect to both cushion cylinder pressure and compressor cylinder inlet pressure



Jan. 16, 1951 R. J. WELSH 2,533,490

GOVERNING OF FREE PISTON TYPE INTERNAL-COMBUSTION COMPRESSORS WITHRESPECT TO BOTH CUSHION CYLINDER PRESSURE AND COMPRESSOR CYLINDER INLETPRESSURE Filed May 23, 1946 2 Sheets-Sheet l Jan. 16, 1951 R. J. WELSH2,538,490

GOVERNING OF FREE PISTON TYPE INTERNAL-COMBUSTION COMPRESSORS WITHRESPECT TO BOTH CUSHION CYLINDER PRESSURE AND COMPRESSOR CYLINDER INLETPRESSURE Filed May 23, 1946 2 Sheets-Sheet 2 m: 63 Q: o #9 8: E8 39 s2.29 2Q Patented Jan. 16, 1951 2,538,490 OFFICE;

GOVERNING OF FREE PISTON TYPE INTER- NAL-COMBUSTION COMPRESSORS WITHRESPECT TO BOTH CUSHION CYLINDER MPRESSOR CYLINDER PRESSURE AND CO INLETPRESSURE Robert James Welsh, Rugby, England, assignor to The EnglishElectric Company Limited, London, England, a British company ApplicationMay 23, 1946, Serial No. 671,767 In Great Britain May 17, 1945Section'l, Public Law 690, August 8, 1946 Patentexpires May 17, 1965 1Claim.

some or all of the air from the compressor serving to scavenge andcharge the engine cylinder.

A device of this kind may be used as a gas generator to supply'anotherpiece of apparatus such as a gas turbine, which may have as its workingfluid either (I) solely air coming direct from the compressor or '(II)solely the exhaust from the engine cylinder (comprising the products ofthe combustion in the engine cylinder mixed with the scavenging airsupplied to the engine by the compressor) or (III) a mixture of theengine exhaust with air coming direct from the compressor. The second ofthese three a1- ternatives is most usual.

If a free piston type internal combustion compressor be used as a gasgenerator to supply motive fluid to a prime mover (hereinafter referredto as a turbine since it will usually take that form) some arrangementis necessary for controlling the output of the compressor in accordancewith the load imposed on the turbine in order to prevent excessive speedfluctuations of the latter or alternatively in some cases such as whenthe turbine is coupled to a ships propeller the output of the compressormay require to be regulated in order that the turbine may run at variouschosen speeds; such an arrangement will usually comprise some form ofspeed governor driven by the turbine.

With free piston gas generators it is known to control the output byregulating the fuel supply to the engine either manually or under thecontrol of a speed 'overnor on the turbine in such a manner as o operatethe generator with a variable length of piston stroke, a long strokeoccurring at the greater outputs as a direct result of the increasedfuel supply to the combustion cylinder driving the pistons fartheroutwards, and a short stroke occurring at lesser outputs due to thedecreased fuel supply associated with lower outputs being insufficientto drive the piston assemblies through the full available length ofstroke.

This method of output 'control has the disadvantage that the range ofout put obtainable is extremely limited because of the inability of thegenerator to continue operating unless the piston stroke be long enoughto provide the necessary scavenge opening through the inlet and exhaustports of the engine cylinders.

It is also possible to operate the control of the output by regulatingthe fuel supply in connection with a volumetric-efficiency regulator forthe compressor (e. g. a variable throttle in the air inlet to thecompressor), whilst maintaining a substantially constant length ofpiston stroke at all outputs. For example, with a decreasing output, asmaller fuel supply will be required and as a result of this smallerfuel supply, the free piston assemblies will tend not to be driven sofar outwards, so that if no other adjustments are made, the stroke willbecome shorter. If, on the other hand, the fuel setting is maintainedconstant and the air inlet throttle opening decreased, the volumetricefficiency of the compressor will be lowered, which will result in-alower mean effective pressure in the compressor cylinder throughout thestroke and if no other adjustments are made then the length of strokewill r increase because, for a constant fuel setting, the

work done in the Diesel cylinder on each cycle (i. e. one outward andone inward stroke) necessarily remains substantially constant and sincethis work has to be absorbed in the compressor cylinder then the lengthof stroke multiplied by the mean pressure in the compressor cylindermust be constant.

A combination of these two eifects can obviously provide a reducedoutput with an approxr imately constant length of stroke. This method ofoutput control has the disadvantage that at all outputs other than fulloutput there is a considerable loss of energy, and consequent loss ofefilciency, arising from the passage of the air through the restrictedinlet throttle.

It is one object of the present invention partially to overcome theaforementioned"disadvantages, and to combine the advantages, of thesetwo methods of control by applying them in such a manner that each ofthem is operative mainly over that range of control for which it is moresuitable while being substantially excluded-allowing for a certaindegree of overlapping-from the range of the other.

The invention relates to a free pistontype internal combustioncompressor in which the control of fuel supply and thus the control ofthe output of the compressor is effected by means which result in thereduction of output from full output down to an intermediate output,being -tion, of a free piston type of stroke anda relatively smallreduction of volumetric emciency, whereas still further reductions ofoutput are associated with a substantially constant length of stroke anda marked reduction of volumetric efllciency.

In order to be better understood and readily carried into eifect theinvention is described in what follows by way of example with referenceto the accompanying drawing of which- Fig. 1 is a diagrammatic view,partly in secinternal combustion compressor according to theinvention,and

Fig. 2 is a diagrammatic view of group arrangement of internalcombustion compressors according to the invention, drawn on a smallerscale. s I

The body I of an opposed piston type free piston internal combustioncompressor encloses the working pistons (2, 2a) and the compressorpistons (3, 3a) whioh'are preferably synchronised by a link mechanism(4, 5, la) and carry at their ends the cushion pistons (8, 8a)respectively, operating in their cylinders (1, 'la). The compressorcylinders are connected, with the usual automatic inlet valves l3 (oneonly of which is shown) interposed, to the inlet manifold (8, 9, 8d),the common entrance 8 of which is con-.

' trolled by a butterfly valve l8. In addition, the

compressor cylinders are connected, with the usual automatic dischargevalves ll interposed, to the transfer pipes (ll, Ila) leading to theusual inlet ports (not shown) of the common working cylinder of thepistons (2, 2a).

The usual exhaust ports (not shown) of this cylinder are connected bythe exhaust pipe [2 to the gas turbine l5, the centrifugal governor l8of which is driven from the turbine shaft, say by means of a bevel gearH. The sleeve l5u, of the governor is under the opposing influences ofthe centrifugal masses I82: and of a spring I80, and operates theaforementioned butterfly valve In through a bell cranklever Illa and alink "lb.

The lever Illa is provided to control the output of the complete plantand is shown as connected to and under thecontrol of the turbinegovernor 1.5. This particular method of operating the output controllever Illa is, however, shown merely by way of illustration and it willbe understood that the output control lever may be equally well operatedby any other means. In the case of a plant intended, for example, formarine propulsion, it will usually be most convenient to arrange forthis lever to-be operated manually by the engine attendant. One branch,say 8, of the inlet manifold is connected by. a pipe l8 to a cylinder IQof a pressure-responsive device containing a piston which is under theopposing influences of the suction coming fromthe inlet manifold 8 andof a. spring 2 I. The opposite end of the cylinder [8 is connected tothe atmosphere by a vent hole l8a.

One of the cushion cylinders, say la, is connected by a pipe 12! to thecylinder 22 of another pressure-responsive device containing a piston 23which is under-the opposing influences of the pressure coming from thecushion cylinder Ia through a spring-loaded non-return valve 24 and of aspring 25. The working side of the cylinder 22 is connected to theatmosphere by a carefully proportioned leak-off 22a while the oppositeside of said cylinder is connected to the atmosphere by a vent hole 22b.Thus the pressure sensitive device will respond substantiallyto themaxi- .nected to the rack 28 in the opposite sense.

\mum cushion pressure of'the immediately preceding stroke as explainedin Patent No. 2,425,850, dated August 19, 1947.

The piston rods of the two pistons (28 and 23) are linked by means ofconnecting rods (25, 28:1,) respectively, to the ends of a lever 21which is pivoted intermediately to the rack 28 of the fuel pump 28. Thearrow and plus sign indicate the direction of movement of the rack inthe sense of increasing the fuel supply.

The two pressure sensitive devices are con- A reduction of pressure inthe inlet manifold 8 will cause the piston 20 to move to the right androck the lever 21 about its connection to link 28a, thereby moving therack 23 in the fuel decreasing direction. A reduction of pressure in thecushion cylinder Ia, will, on the other hand, allow the piston 23 to bemoved to the left by the spring 25 and rock the lever 21 about itsconnection to the link 28, thereby moving the. rack 28 also to the leftand increasing the fuel supply.

The fuel pump 23 is shown, for example, to be operated by a cam 30connected with the twoarmed lever 5 of the synchronising mechanism andacting through rockers (3|, 31a) on the piston rod or plunger 32 of thefuel pump.

The connecting rod 25 carries a collar 28?) which abuts-after a lostmotionagainst a stop 33 which may be fixed or may be the end of a lever(as shown in Fig. 1) acting on a piston 34 in a cylinder 35 where it isunder the action of a spring 38. The cylinder 35 is open to theatmosphere through a vent .hole 35a and is fixed with respect to thecasing l.

The operation of this embodiment of the invention is as follows:

With the inlet throttle l0 wide open the freepistons (2, 3, and 2a, 3a)will tend to reciprocate with an approximately constant stroke by reasonof the connection between the fuel pump rack 28 and thepressure-responsive device (22 to 25) associated with the maximumpressure in one of the cushion cylinders la. Any temporary or accidentaloperation with a greater length of stroke due for example to a slightvariation in the explosive force in the combustion cylinder, tounavoidable inaccuracies in the metering of the fuel by the injectionpump, or to small fortuitous changes in the frictional forcesencountered by the moving pistons, will produce a rise in the maximumpressure in the cushion cylinder la. and will thus effect a reduction inthe fuel supply through the pressure sensitive device (22 to 25) actingon the rack 28 of the fuel pump 29. Similarly any temporary oraccidental operation with a shorter stroke caused by slight changes-inthe various forces acting on the moving parts will result in the fuelsupply being increased, so that in both cases the machine will 'tendtowards operation at a substantially conthe fuel pump rack 28 throughthe link'gear 28a and 21 be regarded as a governing mechanism tending tomaintain a constant length of stroke as explained above, then anydisplacement of pivot 38 by movement of link 26 will have the effect ofvarying the preferred length of stroke which the stroke governingcharacteristics of parts 22 to 25, 25a and 21 endeavours to maintain. Inother words, any movement of link 28 will tend to trim the basic strokelength to which the stroke governing mechanism is set.

In the embodiment shown in Fig. 1. the link '28 can be moved by pistonand will be so moved whenever there is any change in air pressure in themanifold 8-this movement occurring because the air pressure in manifold8 acts on the face of piston 20 through the pipe |8.' Changes inpressure in the manifold 8 will thus produce changes in the preferredlength of free piston stroke which the governing mechanism 22 to 25, 26aand 21 endeavours to maintain. By suitable and obvious proportioning ofthe parts 28, 2|, 21,

etc. it is possible to achieve the desired result of it requiring only arelatively slight drop of pressure in the manifold 8 to effect asubstantial change in the governed length of the stroke of the freepistons.

When the throttle I8 is wide open, the pressure in manifold 8 will beapproximately atmospheric, the rod 26 will be at the extreme left handend of its limit of travel, and as a result the stroke governingmechanism 22 to 25, 26a and 21 will be set to govern the stroke to itsmaximum designed value. Under these conditions the free piston gasgenerator will be runthrottle ID, for example under the action of theautomatic speed governor I6 of the turbine l5 or through a manuallyoperated control (not shown). Slight closure of the throttle l8 willresult in a drop in the absolute pressure in the air inlet manifold (8,8a). This drop in pressure will act on the rack 28 of the fuel pump 29through the pressure-responsive device (I9 to 2 l connected to the inletmanifold 8 and will give rise to a reduction in the'fuel supplysufiicient to reduce the stroke of the free-pistons (2, 3' and 2a, 3a)to less than its maximum designed value and at the same time the newposition of the pivot 38 (which will be further to the right than itsprevious position) will, as previously explained, have the effect ofadjusting the stroke governing mechanism 22 to 25, 26a and 21 toregulate the machine at a shorter length of stroke. This reduced lengthof stroke will result in a lesser delivery of air from the compressorcylinders 39 and 39a, a lesser flow of scavenge air to the engine, alesser flow of exhaust gas to the turbine with a consequent reduction inpower output from the plant.

The reduced mass flow of air consequent on the reduction in length ofstroke will also tend to raise the pressure in the inlet manifold (8,8a) and reduce the loss of volumetric efiiciency caused by the previousthrottling.

If the output of the gas generator be gradually reduced in successivestages in this manner by a step by step movement of the throttle I8towards its closed position then a stage will be reached when furtherreduction in length of piston stroke will not be feasible as the pistons(2, 3, and 2a, 3a) will already be operating with the minimum length ofstroke required to give the requisite operative scavenging opening tothe inlet and exhaust ports in the engine cylinder. When this stage isreached the pressure-responsive device (Hi to 2 I) connectecl'to theinlet manifold 8 should have reached the end of its limited travel, thecollar 28b abutting against a stop 33 which for the moment should beconsidered to be non-resilient. Any further reductions in the airpressure in the inlet manifold 8 will then have no further direct effecton the fuel pump rack 28. Afte this stage has been reached it will stillbe possible to continue to reduce the output of the gas generator byfurther movement of the throttle l8 which will then operate to reducethe output merely by directly restricting and reducing the flow of airto the suction valves of the compressor, thus reducing the amount ofscavenge air supplied to the engine, consequently reducing the rate ofsupply of exhaust gas to the turbine and therefore reducing the poweroutput of the plant.

During this second stage of power output reduction, that is after collar28!: is in abutment with stop 33, the machine will operate at asubstantially constant length of stroke under control of thepressure-responsive device (22to 25) associated with the pressure in thecushion cylinders la. The stroke will, in fact, tend to increaseslightly with increased throttling beyond the stage at which the firstpressure-responsive device reaches the end of its travel. This increaseof stroke will take place because it requires an increase in the maximumpressure in the-cushion cylinder 1a and thus an increase in the lengthof piston stroke to move the piston 23 of the associatedpressure-responsive device (22 to 25) lesser fuel supply.

By an additional feature of the present invention this slight increaseof stroke may beavoided; this is accomplished by providing a certainamount of resilience in the stop 33 which limits the motion of thepressures-responsive device (I9 to 2|). This is achieved in theembodiment shown in Fig. 1 by making the stop 33 a lever acting on thepiston 34 in the cylinder 35 so as to compress the spring 36. Thesuction on the piston 20 is then resisted by the spring 36 in additionto the spring 2| so that even after the collar 26d makes contact withthe lever 33 it will still move, although with a very much reducedsensitivity, in response to further decreases in the absolute pressureof the inlet manifold 8 until the suction on the piston 20 is balancedby the two springs 2| and 36 when the end of the movement of piston 28will be reached. Reductions in manifold pressure after the stop has comeinto operation may thus be arranged to produce no further decrease inthe length of piston stroke, but merely to compensate for the slightincrease in stroke which would otherwise occur.

The invention has been described as applied to a free piston gasgenerator employing a jerk type fuel pump but it will readily beappreciated into a position corresponding to that it may equally well beapplied to machines using the so-called common rail system of injection,or indeed to internal combustion fuel control systems of any known type.Similarly the pressure-responsive devices may ;take other forms such as'that of expanding capsules without affecting the general principlesofthe invention.

The invention is particularly applicable to cases where a number of gasgenerators operate in parallel to supply one turbine. "In such caseseither interconnected individual throttles on each gas generator or onemaster throttle in a manifold connected to the inlets of all gasgenerators will be under either manual control or the control of a speedgovernor on the turbine.

This is shown in Fig. 2, in which, for example, three internalcombustion compressors |0|a, llllb, llllc) are shown so as to representa group of any number of such compressors. Their exhaust tube (I l2a,2b, H20) are connected through a common exhaust tube III to the gasturbine H5 the speed governor ill of which is,

for example, driven by a bevel gear I".

Each compressor has a separate inlet manifold (108a, 108b, l08c)controlled by its own valve (l l0a, I l0b, H00) arranged in therespective inlet tube (M941, 1092), I090) and all linked to the speedgovernor H8 as shown or operated in any other suitable way.

What I claim as my invention and desire to secure by Letters Patent is:

A power plant comprising: at least one free piston internal combustionengine compressor adapted to operate as a gas generator for a gasturbine and including a combustion cylinder, at least one compressorcylinder, at least one cushion cylinder and a fuel supply means; anoutput control system for the said power plant comprising a commonoutput control lever, a throttle at the compressor cylinder inlet of atleast one of the said free piston internal combustion enginecompressors, each such throttle in operative connection with the saidoutput control lever, a pressure responsive device in supply connectionwith the said compressor cylinder inlet, a second pressure responsivedevice in supply connection with at least one said cushion cylinder, afuel supply control lever connected at a point intermediate to its outerends to the fuel quantity control member of the said fuel supply means,a

link member connecting one end of the saidfuel supply control lever tothe first said pressure-aresponsive device, a link member connecting theother end of the said fuel supply control lever to the said secondpressure responsive device, said link members being connecteddifferentially to the said fuel control lever in a sense to reduce thefuel supply both in response to-a decrease in the air inlet pressureandalso in response to an increase in the maximum pressure in the saidcushion cylinder.

ROBERT JAMES WELSH.

REFERENCES CITED v The following references are of record in the file ofthis patent:

' Welsh Aug. 19, 1947

